The necessity for providing sewage treatment plants to clean and purify water discharged from homes and factories is well known. The function of a sewage treatment facility is to receive raw sewage (water containing waste material) as discharged from a city sewage system and clean it to ultimately produce purified water. This is accomplished through a series of biological and mechanical processes.
In a typical water treatment facility, the raw sewage is received from the sewage system and passed through a coarse screen to remove large pieces of matter. The sewage is next directed to one or more primary sedimentation tanks or clarifiers. The sewage remains in primary sedimentation for a period of time sufficient to allow the majority of the heavy matter to settle to the bottom of the tank forming sludge. This sludge is removed for "digestion" by microorganisms. The digested sludge is then dried and can be used as compost or fertilizer. The remaining liquid is treated in a second biological system to remove ammonia. The liquid from this treatment is then aerated and passed into final sedimentation water treatment tanks to remove any remaining solid material.
Water treatment tank configurations vary with each treatment facility application. This notwithstanding, most final sedimentation water treatment tanks are circular. This simplifies automatic skimming, churning and/or bottom scraping operations. More specifically, by eliminating inaccessible corners and providing uniform surfaces, a revolving scraper arm or skimmer blade can provide complete and efficient churning and prevent sludge buildup.
During operation of one type of water treatment tank, water containing sediment enters the center of the tank. In a continuous process, the lighter clean water is effectively decanted from the heavier sediment containing water. More particularly, the clean water is displaced from the tank by the constant flow of water containing sediment into the tank. The displaced clean water is forced to flow under a baffle plate for collecting floating scum and then over a weir, ultimately entering a clean water flow channel. The clean water flow channel directs the water to the next treatment stage where it is chlorinated and further made safe to be discharged into a river or stream.
As is known in the art, the outdoor exposure of the water treatment tanks to direct sunlight encourages the growth of algae. This growth is most prevalent on the baffle, weir, spillway and clean water flow channel. Disadvantageously, algae growth on these members inhibits the flow of clean water from the tank. Further, the algae can be carried in thick masses and high concentrations in the clean water being discharged from the final treatment tank. When this occurs, large concentrations of chlorine are required to kill the algae. Because chlorine is relatively expensive, it is desirable to avoid this problem.
For many years, the removing of algae from the baffle, weir, spillway and clean water flow channel was completed primarily by scrubbing the tank structure with brushes manipulated by hand. Because the final treatment tanks are quite large, this naturally, is a labor-intensive and tedious process, involving a large expenditure of man-hours and cost outlay. Additionally, the algae removing process must be done frequently, thereby further adding to the cost.
Recognizing a need to automate the cleaning process, the present inventor previously patented an apparatus for cleaning algae and debris from a water treatment tank in U.S. Pat. 4,830,748. While this apparatus is particularly effective in cleaning the baffle, weir, spillway and clean water flow channel of a circular tank, it is somewhat limited in application in that it is adapted to be mounted to a revolving skimmer blade. Accordingly, it can only be effectively utilized with water treatment tanks incorporating such a blade. In view of this, a need is identified for a self-propelled cleaning apparatus for utilization with other types of water treatment tanks.